>A few years back I did some research into batteries for an underwater
>propulsion device and I learned that the number of cycles that you got
>out of a battery decreased with the percent discharge of the cycles. So
>I am wondering what the effect on battery life is when you discharge it
>to 5-10% of its capacity. Is that the only way to test the battery?
It's true that a battery's life is improved by limiting the
depth to which you discharge it on each cycle. For example,
it's not uncommon to find a battery rated for say 100 cycles
at 95% of rated capacity and several thousand cycles at 5%
of capacity per cycle. In the ideal situation, a vehicle battery
is needed only to start an engine . . . perhaps 1 to 3% of
capacity and it will indeed run for a very long time for a
lot of "cycles".
Testing a battery for it's true capacity does require a deep
discharge cycle . . . pehaps one every six months or so and
I wouldn't do the first one until the end of one year. The
level of "abuse" to the battery compared to other strains
on its longevity in service is pretty small. I think it's
more important to know the battery's capacity IS than to
worry about squeezing a few more weeks of service out of
it.
Another reader comments ...
"...KNOW ( by measurement)..."
Care to expand, perhaps with particular reference to voltmeters and/versus
ammeters. I'm sure I've seen reference to which of these is the best to
install, but over time I've got confused.
The conventional wisdom for installing electrical instrumentation
on an airplane DOES NOT include a practical means for measuring
capacity. If it were my airplane, I'd have an alernator load
meter and a good voltmeter (0.1 volt resolution) but this is
only part of the task. Having no other tools aboard, I'd pick a
nice day/VFR cross country to shut off the alternator, kill the
main bus, turn on the essential bus alternate feed path and watch
the voltmeter. The goal is to have 10.5 volts or BETTER on the
bus for duration of fuel aboard. 30 minutes out from
a long range destination, I'd turn the alternator back on and
recharge the battery. If the bus voltage is fading at a rate
suggesting that you wouldn't make the field with energy remaining,
then I'd suggest the battery be swapped out.
Now, if you never make long trips or you never fly at night or
the airports you use are non-tower, non-busy fields . . .
perhaps one may settle for less than full-fuel-endurance and keep
the battery in in longer. The important thing is to KNOW how
good the battery is and get rid of it when no longer capable
of meeting your mission.
Bob . . .
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